Metal shader way too dark
pbr shaders need an environment to look more properly. It's one of the key parts in physical based rendering method.
Here is a metal shader under different environments:

to the left we have no environment (black), blender jungle in the middle and blender default room environment in the right.
A quick fix for this would be to add a good environment texture that matches your presentation of the area or comes close to it.
you can start looking for one here: https://hdrihaven.com/